Friday, April 10, 2015

The Brontosaurus Club

By now, anybody who's interested in paleontology, and their mother, and their great uncle, have probably heard the news: Brontosaurus is back!

Of course, the more technically minded paleo fans will know that Brontosaurus never actually went anywhere. Ever since its first specimen was studied in 1879 by Bone Warrior O.C. Marsh, paleontologists have agreed that the species Brontosaurus excelsus* was unique among sauropods. The question soon became, however, exactly how unique. In 1903, Elmer Riggs decided that it was similar enough to another sauropod species, Apatosaurus ajax, that they should both be placed in the same category of sauropods, and since Apatosaurus was an older category ("genus") name than Brontosaurus, he reclassified the species as Apatosaurusexcelsus. However, it was clear even to Riggs that Apatosaurus excelsus and Apatosaurus ajax were different species, and the decision to "lump" them together into one category was always subjective and non-scientific - these kinds of things are a matter of taste only.

So, it was only a matter of time before the discovery of the finer relationships among the various specimens that make up these species prompted some scientists to split them back up. The latest study, by Emanuel Tschopp, Octavio Mateus, and Roger Benson, used a more quantitative basis for splitting and lumping categories of sauropods. They decided that they would split a species into a new genus if it had at least 13 skeletal differences from the next species. At the end of the day this is still totally arbitrary: They could have picked, say, 10 differences, but that would have meant some other species of Apatosaurus would also require a new genus category. As with other category types, like "family" or "order", the "genus" category has no basis in physical or biological reality other than the meaning we assign to it, so in my opinion, we should just drop the whole idea and give each species its own unique combination of names, but that's a topic for another day...

Life restoration of Brontosaurus by Davide Bonadonna,
CC-BY-NC-SA

Back to Brontosaurus: I think that with all the publicity around this study, and the fact that splitting categories is arbitrary to start with, other researchers will be hard pressed to find a good reason for lumping it back in with Apatosaurus any time soon. Like it or not, Brontosaurus is back, probably for good. And who would complain? Brontosaurus is right up there with Tyrannosaurus as one of the best and most iconic and evocative dinosaur names.

But as the details of this new study shows, the iconic Brontosaurus may be back, but it's not exactly better than ever. In fact, only two specimens can be confidently shown to belong to the species Brontosaurus excelsus. The best known and most complete brontosaur-like skeletons, especially the skeleton mounted at the Carnegie Museum, remain in Apatosaurus as the species Apatosaurus louisae (though this might, and probably should, eventually be given its own unique "first name", so it's not Brontosaurus and it's not even the "classic" Apatosaurus.)

My personal favorite "brontosaur" mount, at the American Museum of Natural History, might be a brontosaur, or it might equally be an apatosaur or even a new species. This was the first sauropod skeleton ever put on display, unveiled to the public in 1905, then disassembled and re-mounted 100 years later for a renovation of the museum's fossil halls. In his haste to beat out Carnegie and get the record for first sauropod skeleton on display, AMNH paleontology director Henry Fairfield Osborn didn't leave much time for things like "science" and "studying the fossils". They were collected primarily as a display piece, not an object for research, a fact which makes it very hard to accurately figure out its species. The question of the identity of this iconic skeleton, which I'm old enough to have personally seen in both its old and new incarnations (first with its infamously incorrect head in the old Hall of Jurassic Reptiles and then in its present location in the Hall of Saurischian Dinosaurs), will remain open until somebody gets around to studying it in detail.

A very similar situation exists for another well-known former Brontosaurus skeleton, the one mounted at the Field Museum in Chicago. Like the skeleton at the AMNH, this one needs further study to figure out its species assignment. Other, more recently mounted "brontosaur" skeletons are still brontosaurs in the parlance of the latest study, but they're not Brontosaurus Classic. The skeleton mounted at BYU, for example, is actually an example of Brontosaurus parvus, also known as Elosaurus. If anybody were to follow the suggestion of a unique double name for each species, this skeleton is actually an elosaur, not a brontosaur.

The bizarre head sculpture originally
made for the Peabody Brontosaurus.
Photo by Mike Taylor, CC-BY.

So who's left in the Brontosaurus club? Actually, despite it's widespread fame, there are only two skeletons that can be called Brontosaurus excelsus, the classic species of brontosaur. Both are currently in the collections of the Yale Peabody Museum in New Haven, Connecticut, where O.C. Marsh worked and where much of his fossil collection remains. One of these true Brontosaurus skeleton was once assigned to its own species, Brontosaurus amplus, though the new study shows that these are actually the same species. This second brontosaur is also in the collections at Yale, but is not on display as far as I know (I wonder if bits of it may have been used to help fill in missing parts of the Great Hall skeleton?).

Marsh's original specimen of Brontosaurus described in 1897 (the holotype) is on display in the Great Hall, and has had the same posture since the mount was built in 1926. The only change has been to the head. As with the AMNH skeleton, the original skeleton of this Brontosaurus had a sculpted skull designed to fill in for this missing bit of the skeleton. Whereas the AMNH skeleton's skull was based on skulls of Camarasaurus and Brachiosaurus, the one at Yale was, well, weird. It doesn't seem to have been based on anything except maybe a severe misinterpretation of one of Marsh's early drawings. This was replaced by a cast of an Apatosaurus louisae skull many years later.

The only mounted skeleton of a "classic"Brontosaurus, at the Peabody Museum.
Photo by Ad Meskens, CC-BY-SA.

One irony of the return of Brontosaurus is that, while several of these skeletons were well known for having been given the "wrong" (speculatively restored) heads for many years, we still do not know what the head of Brontosaurus looked like! (Though using the skull of an apatosaur is probably a much safer bet than basing something on a more distantly related camarasaur).

Of course, you can't resurrect a beloved dinosaur name without paleoartists falling all over themselves to create updated life restorations of Brontosaurus classic (which has historically been overshadowed by pictures based on the more complete apatosaur skeletons). My own quick rendition is pictured at the top of the article, not so subtly based on Charles R. Knight's classic but severely outdated painting which has unfortunately been making the media rounds this week. Yes, guys, Brontosaurus is back, but it has certainly been updated since the turn of the 20th century! Be sure to also check out some great modern brontosaur illustrations by Nobu Tamura, Davide Bonadonna (also shown above), and my favorite, by John Conway. One of the key features of both brontosaurs and apatosaurs is their immense, wide, and flat-bottomed necks. Some kind of display function actually seems pretty likely for them!

2 comments:

"They could have picked, say, 10 differences, but that would have meant some other species of Apatosaurus would also require a new genus category."

No. They could have picked 12. If they had picked 12, the other two "major" species of the Apatosaurus complex would have been "split." The other distinguishing value used was 11, for Diplodocus, which they used to keep the rest of the Diplodocus complex together. The value between these is a nice, arbitary, and completely irrelevant 12. In this analysis. At this time. As the authors note, this only works in this analysis, at this time, and that's the ultimate problem with the method:

It defies the principle of developing an objective methodology of distinguishing taxa. It cannot be readily applied to other analyses. It is unscientific.

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About Me

Matthew P. Martyniuk is an
illustrator and science educator
specializing in Mesozoic birds
and avian evolution. He has been
drawing prehistoric flora and
fauna since he first held a pencil,
and became fascinated with the
dinosaur/bird transition after
discovering a copy of Gregory S. Paul’s Predatory Dinosaurs of
the World at his local library. His
illustrations and diagrams have
appeared in a variety of books,
news articles, and television
programs from Discovery, the
Smithsonian, and the BBC, and
he publishes the paleontological
blog DinoGoss.